Treatment of paper and the like



J. 25; .1943. J. v. BAUER ETAL 9 1 v TREATMENT OF PAPER AND THE LIKE Filed Oct. 6, 1958 acid. 1 x The treatment of paper with'resinous con- Patented '26, 1943'.

Y zsqaoso i raua'rnanr orrarnnaim Jordan V. Bauer, Elmwood Park, and Don. M. I Hawiey, Geneva, 111., assignors' to Stein, Hall Manufacturing Company, Chicago, 11]., acor poration of- Delaware 1 Application October 6,1938, Serial No. 233,557 51 Claims. (Cl. 111-155).

This invention relates .to an improved method of treating cellulosic materials and tonew-and improved products obtained thereby, The invention is particularly directed toward. the treatment of water-permeable'pulped 'cellulosic fibers which may be in the former" relatively loose porous fibers, or in the form of a molded article, or still more desirably in sheet form, as'in paper.

It is well known in the art to treat cellulosic materials with formaldehyde or. with formaldehyde and an acid, or with resinous condensation products formed from urea and formaldehyde.

The methods of treatment proposed so far, however, leave. much tov be desired from the standpoint of ease of application-results obtained and low cost.

factors.

For a long time it has been known that the treatment of paper with formaldehyde and an acid followed by the application of heat would produce a paper product of improved wet strength characteristics, but this method of treatment has cause p per when so treated becomes brittle and is therebymadev unsuitabl for most practical p r ses. Embrittlement also occurs when paper is. subjected to heat in the presence of a condensation product of densation products of urea and formaldehyde is described by Ellis, ,"The Chemistry .of Synthetic For this reason, 'none of the prior art procesSesh'as attained success in those fields.

of usage mentioned herein where low cost, sim- I plicity and commercial practicability are primary urea, formaldehyde and an pressure, and the products obtained'are still, hard or brittle. v

It may be noted at this point that the present invention deals with thetreatment of' water-. vpermeable pulped cellulosic fibers, as distin guished, for example, from textile materials and cellulose in the form of thick boards, wooden panels, and the like.

One of the objects of this invention is to provide a new and improved method of treating celluloslc fibers in water-permeable form in order to obtain new and-improved products; Another object is to provide a method of treatment which is characterized by simplicity, practicability and vnever had any practical commercial success be-'-" Resins," vol. '1, ages 642 a, 644 1935). Accord! ing to one method described, papervresembli'ng ,glassine may be obtained by adding a gel of urea-formaldehyde condensation product to the pulp in the beater. By anothermethod, paper is,dipped in a resinous urea-formaldehyde com-y position and subjected to heat and pressure, thereby producing a smooth lustrous sm'iace. By

another method, transparent paper may be prepared by treating parchment paper with a ureaformaldehy'de condensation product,.dr'ying and heating at 120 to 150 C. Br still another method, porous panels of celluloslc fibers can be impregnated with an alcoholic solution of eurosformaldehyde condensation product which is later economy. Still a further object isto provide a new and improved method of treating paper and similar pulped forms of cellulosic materials.

' An. additional object is to provide a new and economical method of producing water-absorbent or water-permeable cellulosic sheet materials which are characterized bya higher Mullen test than the untreated materials either in water dry state,.and by greater wet strength and scuff-- resistance, but at the same time are not rendered brittle by the treatment. Other objects will appear hereinafter. a I In accordance with the invention, we have found that paper articles or sheets formed from jcellulosic pulped fibers in porous or water-permeable form may be converted to new and improved products by subjecting said cellulosic materials to treatment with a formaldehyde compound, 'a urea and an acid reacting substance in the presence of water and confining the treated fibers in a state of equilibrium with the treating materials substantially at normal or11oom temperatures until said fibers have reacted with the formaldehyde compound and urea and have been rendered less capable of being hydrated.

, It is important in our invention that the formaldehyde and urea. be in a'water-soluble form as distinguished from the water-insoluble form which characterizes urea-formaldehyde resins in their later stages of formation. .We preferably add the formaldehyde compound, urea and acid reacting substance to the cellulosic fibers in submade insoluble by heating at C. Still other applications of urea-formaldehyderesins to Paper are described, but in every case the treatment" described involves the use of heat or of heat and stantially unreacted state. If the formaldehyde compound, urea and acid reacting substance are reacted or partially reacted before addition to the cellulosic fiber, thickened or relatively viscous solutions are formed which are less capable of penetrating the cellulosic fiber and hence tend to give merely "a surface eii'ect. Moreover, unless proper proportions of formaldehyde and urea are used, as more fully hereinafter described, precipitation of an um'eactive condensation product A will occur, thus causing a loss of materials.

-may be effected in a number of ways, depending upon the type of material treated. For example, if the material treated is a sheet of paper, the treated fibers maybe confined in a state of equilibrium with the treating materials by winding. the treated sheet into a roll immediately after it has been treated. Alternatively, the treated sheets may be kept in juxtaposed relationship by pressure or otherwise so that each sheet is closely associated with a similarly treated sheet. If the article t6 be treated is made from molded pulp or molded fibers, confinement after treatment may be eflected by stacking the articles in nested relationshipaaanother method of confinement is to keep the fibers or articles formed therefrom in a bath in contact with the treating materials until the reaction is substantially complete. Since for-the purpose of our invention the reaction must be carried out at substantially normal temperatures, this will require an extended period'of time. All of .the I methods of confinement chosen, however, are designed to maintain the presence of sumcient moisture to enable the reaction to proceed and to obtain uniform and thorough penetration of the reacting materials. Unless some method of confining the treated fibers in a state of equilibriumwith the treating materials is provided,

the desired results are notobtained. Our preferred methods of confinement-involve winding 9. treated sheet into a roll, orotherwise bringing l a treated article into juxtaposition with similarly treated articles as distinguished from those methods which involve the use of a saturating bath. The latter type of method, however, has

some advantages with certain special types of treatment.

In practicing our process we have been able to obtain flexible absorbent paper which apparently possesses all of the attributes and qualities of the original untreated paper .with some additional characteristics that renderit suitable for purposes hereinafter described. Among these additional characteristics are a high wet strength which is not merely a surface effect but which is distributed uniformly throughout the sheet. Furthermore, we have found that the scuff-resistance is increased and that the Mullen test is increased when the paper is in the dry state as well as when it is in the wet state.

We have found, moreover, that a very definiteeffect on the paper can be obtained by using relatively small amounts of urea, formaldehyde and acid. Thus, by merely dampening the surface of the paper sheet with urea, formaldehyde and an acid solution andimmediately winding it into a tight roll and allowing it to stand for a period of time, we ar able to obtain a uniform action on the paper fibers throughout the sheet without greatly increasing its moisture content and necessitating a drying operation. This feature makes the cost of treatment very low and nables available commercially because of the low cost of treatment.

This is an extremely important factor because such products are ordinarily used in fields where a substantial increase in cost would be prohibitive to their use.

In carrying out our process we ordinarily apply'the urea and formaldehyde in water-soluble form and the acid in the form'of a solution either by means of a spray or a kiss roll, although it will be understood that any other suitable means may be used. Many variations may be used in adding the various materials to the cellulosic fiber, paper sheet or the like. For instance, the formaldehyde in the form of a commercial aqueous solution, a solution of urea and a solutionof an acid reacting substance may all be added separately to the paper sheet.

In accordance with the invention, we preferably add one or'more of these materials from opposite sides of a paper sheet. If a one-sided effect is desired, however, we may add them all from the; same side, 1 The addition in either case may be'simultaneous or successive. The urea and formaldehyde may be mixed together and added to one side of the sheet and an acid reaway from the formaldehyde until it is on the paper. We have found that urea and formalde-- hyde when brought together in proportions of, 'say, 2 moles of formaldehyde to 1 mole of area tend to form a white precipitate which is. in-

soluble in'water and substantially of no value in our process since even if incorporatedx'inte the paper fiber it can act only as a filien lt.

will be apparent that if a portion of the reset ing materials is to be removed by a white unreactive precipitate, the cost of treatment may be substantially increased. For this reason, where we mix the urea and formaldehyde together prior to addition to the cellulosic fiber, we preferably employ an excess of formaldehyde greater than 'about 3 moles per mole of urea.

We have also noticed that the addition of an acid to the urea and formaldehyde when less than 3 moles of formaldehyde per mole of urea are employed, tends to increase the rate of formation of the white precipitate mentioned above but with the use of an excess of formaldehyde, as stated above, it makes no difference as far as the formation of a precipitate is concerned whether the acid is added at the same time as the formaldehyde and urea or later.

Regardless of whether we add the formaldehyde separately or with the urea to the cellulosic fiber, we preferably make a separate addition of a material which is adapted to react with and remove excess of formaldehyde. For this purpose we preferably employ a material which is nonreactive with acids, such as urea or thiourea, and such material may be incorporated with the acid and added to the opposite side of a paper sheet. Alternatively, we may employ a reactive material, as, for example, amines such as diethanolamine,

ate and other substances capable of neturalizin the excess formaldehyde. In this case the neutraliz ng ent has to be added after the acid because otherwise it would react with the acid. This latter method is more particularly adapted to the bath type of confinement previously described.

One method of avoiding the use of an excess of formaldehyde is to add the materials separately to the paper, preferably at practically the same time; Likewise, simultaneously adding and mixing the urea and formaldehyde avoids precipitation and makes it unnecessary to use an excess of formaldehyde.

The selection of a suitable acid is of outstand ing importance in carrying out our invention. We have found that the hydroxy carboxylic acids,

' particularly lactic acid, are eminently suitable for our method of treating cellulosic fibers. Generally speaking, the acid chosen should be one which penetrates a water-permeable cellulosic fiber with ing materials to the same side of the sheet. An alum solution, or similar acid salt solution, is used in this instance beacuse it does not have the property of readily penetrating into the paper strucgreat rapidity. Certain inorganic acids such as phosphoric acid have this property but are less desirable than the organic acids.

formaldehyde in water-soluble state, which do not We have further found that syrupy solutions of urea and' form precipitates, may be prepared with acids such as lactic acid and limited amounts of water. These solutions tend to thicken further when cooled.

As already indicated, we may treat pulped cellulosic fibers in a bath of acid, urea and formaldehyde, all of said ingredients being in watersoluble state, or we may subject the articles to immersion in'a bath of urea and formaldehyde and later spray them with an acid or with an acid and'urea, orwith an acid followed by treatment with another material reactive with formaldehyde such as a weak base, an amine or the like. The treated materials are then squeezed, if possible; or washed free of any excess unreacted materials. It will be understood that all of said methods include a confinement treatment at substantially normal temperatures until the reaction is substantially complete. In no case do we heat the.

treated cellulosic fibers while an acid is present therein because we have found that subjection of materials which have been treated with urea, formaldehyde and an acid to heat or to heat and pressure, hardens and embrittles the cellulosic While our method is preferably usedin the treatment of unsized cellulosic fibers, we have ture and as a result, only the paper fibers adjacent the surface of the paper are acted upon.

The invention will be further illustrated by the following description in conjunction with the accompanying drawing, in which:

Figure 1 represents an apparatus suitable for treating a cellulosic sheet material in accordance with our invention where the cellulosic sheet has already been formed and wound into a roll;

Figure 2 illustrates another'form of apparatus for incorporating materials into a cellulosic paper sheet in accordance with our'invention;

Figure 3 illustrates a third form of apparatus for incorporating materials into a cellulosic paper sheet according to our invention wherein the materials are added from one side at the nip of a roll; I

Figure 4 is a plan view illustrating a modified form of our invention adapted to be used when one or more solutions are sprayed on a paper sheet, as herein provided;

Figure 5 illustrates an elevational sectional view of the apparatus shown in Figure 4.

As shown in Figure 1 apaper sheet or other of the paper sheet A, in accordance with this invention, from said rolls 6 and I2. In order to provide a uniform coating, solutions are introduced through felts 26 and 28 associated with rolls 6 and 12, respectively. The felts are kept 6 and I2.

felts 26 and 28 through which the solutions may.

also used it in the treatment of rosin sized papers. I

treated with our process it is necessary in order to obtain satisfactory penetration of the treating solutions into the sheet, to incorporate with each of the solutions a small amount of acetic acid or other acid adapted to cut the sizing materials.

Although for most purposes it is desirable to -produce a paper sheet wherein the paper fibers 3"5 ,have been acted upon throughout, it is possible that for some purposes a paper sheet may be desired where only the paper fibers adjacent the surface of the sheet are to be acted upon. This can be readily accomplished by our method of treatment by using an acid salt solution such as an alum solution instead of a penetrating acid such as lactic acid and applying all of the reactsupplied with solutions through conduits 30 and 12 associated with felts 26 and 28, respectively.

In this way it is possible to control the exact to the paper sheet A.

It will be understood that other means may be provided 'for adding a material by means of rolls For instance, instead of providing be applied to rolls 6 and I2, said solutions may be introduced into vessels 22 and 24 and doctor rolls provided instead of felts 26 and 28.

described in Figure 1 is as follows. The sheet of paper A is unwound from a roll 2, passed between guide roll 4 and over coating roll 6 where the under side of the paper is coated either with an acid solution, a urea solution, or a mixture of urea and formaldehyde, or a formaldehyde solu-- tion, the choice of a particular solution being based upon the considerations previously outlined. The treating operation is efiected by direct contact between roll 6 and paper sheet A at the upper surface of roll 6. As roll 6 rotates it is supplied with the treating material through flt 26 which in turn i supplied with the treating material through a conduit 30 leading to a source of supply, not shown.

After paper sheet A leaves roll 6 it passes over another guide roll 6 and thence around a third guide roll in to coating roll i2 where the previously untreated top surface of the paper is treated with one or more additional reacting materials. These additional reacting materials are supplied to roll l2 through felt 28 which in 4 posite' sides of the paper.

shown in which paper sheet A from a roll '34 is passed betwden two sprayers 36 and 38 adapted to spray materials onto the paper sheet from op- Acoording to this method a solution of urea can be introduced to spray 36 from conduit 40 and a solution of formaldehyde introduced to spray 36 from con- -.duit 42 and immediately sprayed upon paper A, depending largely on the amount of material] which it is .desired to apply. The rolls themselves may be run at different speeds from each other. In anycase, it is preferable that the speeds of the rolls and thespeed of the paper sheet be ccordinated bya coordinating means of any type such asis well known to those skilled in the art and that the same relative speeds-of the two rolls be maintained for any given operation.

In supplying the treating solutions to a paper sheet, as above described, it will be recognized that many different procedures may be adopted. For instance, an unreacted mixture of urea and formaldehyde may be added to a sheet, A by means of roll 6 and an acid solution added to the opposite side of the sheet from roll I2, or the solution added at roll 12 may comprise urea and an acid, this being one of the preferred procedures. Alternatively, a solution of formaldehyde and an'acid may be added at roll 6 and a solution of urea at roll I2, or a solution of formaldehyde may be added at roll 6 and a solution'of urea and an acid at roll 12. We have found that the preferred proportions for reaction between the cellulosic fiber, urea and formaldehyde correspond to a ratio of about 1 mole of urea to about 1:2 moles of formaldehyde, but if the urea and formaldehyde are added together and are mixed prior to the addition, then we preferably employ at least 3 moles of formaldehyde per mole of urea to avoid the precipitation previously mentioned. Where an excess of formaldehyde is used over that required to react with the cellulosic fibers, we prefer to remove said excess by a further reaction with urea and for this reason, where we add formaldehyde or urea and formaldehyde at one point, or to one side of the paper, we preferably add additional urea at another point or to another side of the paper.

As paper sheet A leaves roll I! it is passed over sheet A as soon as the urea and formaldehyde are brought together. To the opposite side of paper sheet A a solution of an acid and urea may then be applied, or if it is deemed unnecessary to remove any unreacted formaldehyde, an acid solution alone may be applied, said solutions being applied from spray 38. Paper sheet A is then passed through rolls 44 and 46 which act aspress rolls,,smoothing rolls and guide rolls. The paper sheet is rewound' on roll 48, which is mounted on a suitable support 50, asshown. After being wound, roll 48 is allowed to stand at substantially normal temperatures until the reaction is substantially complete and the fibers in the paper are rendered less capable of'being hydrated. 1

The arrangement shown in Figure 3 represents another modification of the invention in which paper from roll 52 is passed between guide rolls 54 and 56 and to'rewinding roll 58. Just before the paper reaches rewinding roll 48 it'is sprayed with solutions made up of urea. formaldehyde and acid reacting substances. These solutions are introduced to spray 60 from three conduits I 62, 64 and 66, one of said conduits carrying an acid solution, a second a urea solution, and the third at formaldehyde solution. In this way the urea, formaldehyde and acid are brought together practically simultaneously and immediate- 157 appliedto paper sheet A before any substantial reaction can take place between the urea and formaldehyde to form a white precipitate in the manner previously described. As the materials are applied to paper sheet A they are immediately wound into roll 58 and since they are applied substantially at-the nip of the roll, opposite sides of the paper sheet containing the applied materials are brought into contact with each other and confined in such close relationship as to ina series of guide rolls l4, l6 and I8 and then resure uniform and thorough penetration. As roll 58 is allowed to stand, reaction takes place rendering the cellulosic fibers water-resistant without substantiallyafiecting the paper in such a way as to render it-non-flexible. As shown in tact with the bottom side and vice versa, thus bringing together the acid reacting materials, the

I urea and the formaldehyde into relatively close relationship and thereby greatly facilitating a reaction adapted to increase the water-resistance of the paper. Since according to our method we preferably add very little treating material to the and insures uniform distribution throughout. i

The speed of reaction may be increased somewhat by the tightness with which the roll 26 is wound. 6 After the rewound roll has been allowed to stand for several days or for even a lesser period, the paper is ready for use. Examination of the paper at this point shows that it is less capable of being hydrated. Its Mullen tests, both'dry and wet, have been increased, and it has greater resistance to send and puncture.

In Figure 2 a modified form of the method is the drawing, rewinding roll 58 is supported by a support 68 or any other suitable'meansmay be used for this purpose.

The apparatus illustrated in Figure 4 isanother preferred embodiment of the invention which may be used in order to obtain uniform distribu-- tion of applied materials when such materials are applied from a spray. The View shown in Figure 4 is a plan view of the apparatusshowing paper sheet A passed beneath curved shields l0 and I2. Spray 14 is placed centrally between said shields. Urea, formaldehyde and an acid; all in solution form, may be introduced to spray 14 through one, two or three conduits in any suitable manner. It is well recognized that a spray tends to distribute more material near the center of the area sprayed than toward the edges. Curved shields I0 and 12 tend to prevent this by limiting thearea. of paper sprayed near the center of the spray and gradually increasing the area sprayed toward the outer portions of the sprayed area. In this manner uniform distribution is assured. Any material'hittina the sides of shields I and 12 is carried downwardly into troughs I and 18 and, if desired, returned to the spray in any suitable manner through conduits I0 and 82. Figure 5 is across-section taken centrally through'Figure 4, showing spray ll, shields and 12 and troughs 80 and 82 positioned above paper sheet A.

It will be understood ject to some variations that our invention is subas to the proportions and amounts of material and the types of material 10 employed. While we preferably employ urea we may use its water-soluble analogues and homologues having substantially the same characteristics, as, for example, thiourea. Likewise, instead of formaldehyde we may use formaldehyde 5 compounds which react similarly to formaldehyde, as, for example, paraformaldehyde and ace-' .taldol. The formaldehyde used may be anordiaqueous solution tration having a specific gravity According to our preferred ment wherein we add solutions of amounts of a urea, an acid reacting of from .75 to .81. method of treatrelatively small grade of formaldehyde such as is sold in of about 30% to 40% concensubstance and a formaldehyde to the paper, we prefer that not 4 more than about 8% to 10% additional water be papen, thus added, based on the weight of the making it. unnecessary to dry the sheet after treatment for most purposes. In some instances, however, as already described, treatment by confining the paper fibers in a bath of the treating material substantially without heatingv until reaction is substantially complete.

It is preferable in accordance with our invention that the total increase in paper due to the addition of urea, aldehyde and acid be not more than about 15% and not less than about 1%. where water-permeability, flexibility not of primary. said materials up to or higher, may be employed. For high wet strength coupled with good flexibility, we preferably employ said added substances in an amount sufllcient to increase the dry weight of paper by about 2% to about 5%.

We have mentioned that the acid reacting sub-. stances employed are preferably acids capable of penetrating cellulosic fibers rapidly, and particularly lactic acid. As a class we prefer the hydroxycarboxylic acids, including monohydroxy monocarboxylic acids, e. g.,-' glycolic and lactic; monohydroxy-dicarboxylic acids, e. g., malic, tartronic, glutaric; monohydroxy-tricarboxylic acids, e. g-., citric; polyhydroxy-monocarboxylic acids, e. g.. glyceric; polyhydroxy-dicarbozwlic acids, e. g., tartaric, hydroxy citric, glutonic and mucic. Other acids which have been found to be suitable are the organic sulphonic acids, particularly aromatic sulphonic acids, as, for example, benzene sulphonic acid, ilar acids.

-As previously stated, acid salt solutions may be employed instead of the free acids, particularly where a one sided effect is desired.' The term "acid salt solutions" of salts in water which have a pH less than 7. In addition to alum, which has already been mentioned, other examples of such solutions are ammonium chloride, ammonium sulfite, ammonium bromide, ammonium chloride and ferric chloride. Amine salts having we may effect the the dry weight of 5 proved box board liners, wall paper, wrapping paper, paper to be used in making laminated paper board, newsprint, book and magazine papers, molded paper pulp articles, paper twine and cord, paper reed furniture, paper shoe soles, bag papers, paper tape, paper gaskets, paper insulating material, tissue papers, including cigarette papers, paper drums and containers, paper receptacles, paper building materials, paper filters, corrugated papers and corrugated paper board. Our invention is of outstanding importance for the preparation of papers which are required to be water-absorbent and at the same time have a high degree of wet strength, as, for example, paper toweling. Among other things, we have found that our method of treatment, while increasing both the wet and dry strength of paper toweling. does not destroy its absorbency but on the other hand, if anything, greatly increases the rapidity with which it will absorb moisture. While the invention is not limited to any theory,

this is probably due to the fact that paper towelnot as rapid as might be desired. Furthermore,

' it is possible that the fibers themselves may contain cells which tend to absorb moisture but because of their structure the rate of absorption is relatively low. Our method of treatment apparently changes the structure of toweling and similar water-absorptive materials so that the water may more easily penetrate the spaces between the the cells within the fibers themselves. It may be that our treatment is more effective because it lowers the surface ,tension of oellulosic materials, but in any event, defflbers and perhaps lnitely improved results are obtained and paper and water-absorptive characteristics are importance, larger percentages of -40 *toweling prepared as herein described may be used without tearing and without leaving remnants of the toweling on the hands or face of the toluene sulphonic acid and simis used to describe solutions iodide, aluminum an acid reaction at the tempeatures employed be prepared in and im- Reference is hereby made to our co-pending application Serial No. 233,556, flied of even date herewith, in which the claims are directed toward a method and apparatus for making paper of improved wet strength on the paper machine. Having thus described the invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A method of treating normally water permeable paper of relatively low wet strength in order to increase its wet strength without substantially decreasing its water absorptivity which eomprises treating said paper in sheet form with a formaldehyde compound, urea and an acid reacting catalytic substance capable of penetrating the paper rapidly, said materials all being added separately and uniformly to the paper in solution form, the urea being added to the opposite side of the paper from the formaldehyde compound, and then immediately winding said paper into a tight roll, said treatment and said winding being effected substantially without heating while maintaining a moisture content within the range of about 3% to about 10% by weight of the paper and employing resin-forming proportions of urea, formaldehyde and acid catalyst in amount to increase the dry weight of the paper within the range of about 2% to about 5%, said paper being characterized by the fact that the wet strength and resistance of the paper to tearing while wet are substantially increased after the paper has been allowed to stand in roll form for a substantial period of time without substantially decreasing the water absorptivity of the paper.

2. A method of treating lr'ra'it paper inorder to increase its wet strength without substantially decreasing its water absorptivity which comprises treating said paper with resin-forming proportions of a formaldehyde compound, a water soluble urea and an acid catalyst, at least one of said materials being added to the paper separately from the others, said materials being added in amounts to increase the dry weight of 5. in a method oi'treating a water; permeable pulped cellulose in sheet form, the steps which comprise subjecting said pulped celiulosefsheet to treatment with a formaldehyde compound, a

watersoluble urea and an acid'catalyst in the presence of moisture, the amount of. iormalde hyde being in excess of about 3 moles of formaldehyde per "mole of urea,.adding an additional amount 01- urea in-a separate phase sufficient to react with any excess formaldehyde, the total amount of added materials being not less than the paper within the range 01 not less than about 7 2% and not more than'about'; 5% and immediately winding said paper which has been so treated into a tight roll before any substantial resin-forming reaction has occurred and substantially without heating.

3.-' A method of treating a to increaseits wet strength without substantially decreasing its water absorptivitywhich comprises treating said pape'r'in sheet form with resini'orming proportions of aiormaldehydecom pound, a water soluble urea and an acid catalyst capable of penetrating the paper rapidly, at least one of said substances being added to the paper' in a separate phase from the others,-th e mois-' ture content or said paper being within the range of about 3% to about during. the addition of I saidsubstances and the total amount of said added substances being not less than about 2% and not more than about 5% based uponthe-dry krait paper in order about 2% and not more than about 5% based on the dry weight of the paper, and confining said treated fibers'together in closely associated relationship at substantially normal temperatures until said cellulose fibers have been rendered less capable of being lwdrated, the resultant sheet being characterized by increased scufl resistance weight otthe paper, then'immediately winding said treated paper into a'tight roll and allowing said paper to standin rolled torm tor a substantialperlod of time substantially without heat- 7 ing, the paper thereby'obtained"having an increased wet strength and resistance to'tearing while wet with substantially unimpaired water absorptivity. and water permeability.

4. In a method of treating water permeable pulped cellulose fibers in sheet form, the steps which comprise subjecting "saidfibers to treatment with a formaldehyde compound; a water soluble urea and a hydroxycarboxylic acid catalyst, said treating substances being employed in resin-forming proportions with the total amount thereof not less than about 2% and not exceeding about 5% of the dry weight of the paper, and

confining said treated fibers together in closely associated relationship at substantially normal temperatures until said cellulose fibers have been rendered less capable of being hydrated.

- water soluble urea added together in water soluble'iormand an acid catalyst added separately, said materials being added in amounts to increase the dryweight oi the paper within the range of not less thanv about 2% and not more than 5%, and' immediately winding said paper which has 4 been so treated into a tight roll beioreany substantial resin-forming; reaction has occurred and substantially without heating. i v

7.111: a method of treating water-permeable pulped cellulose fibers in sheet form, the-steps which comprise subiectin'g'said fibers to treat-:

ment with a formaldehyde compound and a water soluble urea added-together in a water soluble form and a hydroxycarboxylic acid catalyst added separately, said treating substances being employed in resin-forming proportions with the total amount thereoinot less than about 2% and not exceeding about 5% of the dry weight of the paper, and confining said treated fibers together in closely associated relationship at substantially normal temperatures until said cellulose fibers have been rendered less capable of being hydrated.

' JORDAN v. BAUER.

DON M. HAWLEY.

. -i CER IRIQATE OF comcnon;

'. Patent no; 23095090. "Januar 26,1915, 7

It is hereby certified that efror' appears inv the printed specification of the above numbered patent requiring eorre'ction c-s foliowe-z Page 2, first column, line 10, for 'charige$" 'zpead --,ohang.e"-- page 5, second colfimn line 5, for -"beacus e" read b'e'cause-- page-)4, fifst column, line 611. for "loosely" reed "closelypage 5, first colunin; "111E 58, for where read f-where---; line'72, for "temoeatui'es'f tread "temperatures"; and that the said Iettefs Pateh't -sh'o1i1d pe read with thi'jcoi-rec tion therein that the same may conform to the fecord of the case 'inthe Patent Office.

Signed and sealed. this 50th day of Harch, A.,D. 1911.5. I

Henry Van Arsdale, i1) Acting Commissioner of Patents. 

